1. Field of the Invention
The present invention relates in general to telecommunications systems and, more particularly, to a method and apparatus for sharing one or more telecommunications channels among multiple users.
2. Prior Art
Subscribers to telecommunications services are offered a wide array of different kinds of services from a multiplicity of vendors. Wide Area Telephone Service (WATS), Foreign Exchange Service (FEX), and plain old telephone service (POTS) are examples of services offered to the public.
The services are provided over either a leased or a dial-up line. A leased line is one which the subscriber contracts for on a monthly basis, while a dial-up line uses the carrier circuit-switching facilities to establish a circuit every time the subscriber wants to communicate between specific transmitting and receiving locations. In either case, one or more telephone lines are brought to the subscriber's home or office so that the subscriber may interface with the telephone system.
At the subscriber's premises, the subscriber has, many times, a variety of different needs for using the telephone line. For instance, the subscriber may need to use the line for voice communication using a telephone or for data communications through a modem. In other situations, a subscriber, such as a large business, may have one or more host processors having many applications which need access, from time to time, to a telecommunications channel via a communications controller. A telecommunications access method, such as IBM's Virtual Telecommunications Access Method (VTAM), resides in the host processor and provides an interface between the host processor and other resources in the communications network.
FIG. 1 illustrates, in a simple block diagram, communications between a number of host processors and the communications network. A number "N" of physical line ports 10 are connected at the subscriber's premises 12 for connection to the communications network 14. Each host processor 18 has an associated communications access method (AM 1, AM 2, . . . AM N) 20. Examples of communications protocols supported by the various access methods include SNA, TCP/IP, and OSI. Each access method 20 supports a plurality of applications (A 1, A 2, . . . A z) 22 which need access to the telecommunications network 14. Examples of situations where an application needs access to the telecommunications network include a stock broker needing to access real-time stock prices and a doctor wishing to obtain a patient's records located at the main hospital across town. FIG. 1 is shown as an example of a network configuration. Networks may be confiqured in many other ways: for example, a host processor may have more than one access method.
Each access method 20 "owns," or controls, one or more of the physical line ports 10 for allowing an application to access the communications network. The number of line ports 10 and the type of service supported on each is dependent upon the extent and type of use by the host processor 18 and the access method 20. Until now, there was no way for the different communications access methods (different protocol stacks) to "share" a line port without the access methods actively sharing information with one another. Because access methods are not designed to coordinate their use of network resources with one another, telecommunications lines cannot be shared between them.
In other words, an application using one access method could obtain access only to the communications channels controlled by that one access method. The application could not access other communications channels controlled by other access methods. This is the result of the access methods not being designed for communicating with one another. As an example, an application operating on VTAM using IBM's System Network Architecture (SNA) can obtain access to the telecommunications network only via the telecommunications channels controlled by the VTAM. VTAM cannot obtain access to the telecommunications channels controlled by other access methods such as TCP/IP or OSI. Thus, the line ports which are paid for by the subscriber cannot be optimally used, as the telecommunications activity cannot be distributed among the available lines. Rather, some lines may be idle while others are congested.
This problem, until recently, was not serious as the cost of leasing the line ports and their associated services was relatively inexpensive. This problem, however, is especially exacerbated with the advent of the Integrated Services Digital Network (ISDN).
With ISDN, voice and data are integrated over digital lines thereby promising to replace multiple (often under-utilized) dedicated voice and data lines entering customer premises with one or a few lines using ISDN technology. Using the ISDN basic rate interface (BRI), the same wires which once could carry only a single voice conversation (or a data call simulating voice with a modem) now can carry two individual voice conversations and a separate signalling or data transmission. With basic rate access, one "D" channel (which is available for signalling and data) and two "B" channels (which each can carry an independent voice or data call) can be utilized at the same time on the single telephone line. The ISDN primary rate interface (PRI) offers twenty-three (thirty in European systems) B channels and one D channel and is designed for customers requiring greater capacity than provided by the basic rate interface. Thus, through the use of either the ISDN BRI or ISDN PRI, multiple applications at the ISDN subscriber's premises could access the same telephone line at the same time.
Presently, however, the physical port through which the subscriber obtains the ISDN service can be controlled by only a single access method. For example, where a customer subscribes to the ISDN PRI service, it has access to twenty-three independent B channels and one D channel. The customer cannot however distribute access to those channels over several access methods, because one access method controls the physical port. This is quite inefficient: one physical port at the user's premises may be fully utilized while others may be at least partially inactive. Using the present technology, the applications of the first access method have access only to their dedicated port and not to the remaining physical ports.